Crohn's Disease vs Ulcerative Colitis: How They Differ

Last updated: 29 Oct 2026

Crohn's disease and ulcerative colitis are the two main types of inflammatory bowel disease (IBD). Both are long-term conditions in which the immune system causes inflammation of the gut, and both tend to come and go in flare-ups and quieter spells.[1][2] They share many symptoms, so people often wonder how Crohn's vs ulcerative colitis compare. The main differences lie in where the inflammation happens and how deep it goes, and those differences shape the tests and treatment a doctor may recommend.

If you're still trying to work out whether bowel symptoms could be IBD at all, our article on IBS vs IBD is a good place to start.

Crohn's disease and ulcerative colitis at a glance

What is Crohn's disease?

Crohn's disease is a long-term condition in which part of the gut becomes inflamed. It can affect any part of the digestive tract, from the mouth to the bottom (anus), and the symptoms depend on which part is affected.[3] Inflammation can appear in patches, and it can extend through the whole thickness of the bowel wall.[4]

There's currently no cure, but treatment can help people stay free of symptoms for long periods.[3] Symptoms most often start in teenagers and younger adults, though Crohn's disease can begin at any age.[3]

Crohn's disease symptoms

Common Crohn's disease symptoms include:[3][7]

• diarrhoea
• tummy pain and cramping
• blood or mucus in the stool
• feeling very tired or generally unwell
• loss of appetite and losing weight without trying
• pain around the bottom.

Some people have constipation instead. Children may not grow as expected.[3] Crohn's disease can also cause symptoms outside the gut, such as joint pain, red or sore eyes, skin changes and mouth ulcers.[3][7]

What is ulcerative colitis?

Ulcerative colitis is a long-term condition in which the colon and rectum become inflamed. Small ulcers can form on the lining of the colon and may bleed and produce pus.[5] The inflammation always starts at the rectum and can spread continuously up the colon. How far it reaches varies from person to person.[6]

Unlike Crohn's disease, ulcerative colitis doesn't affect the small intestine or other parts of the digestive tract.[4][6]

Ulcerative colitis symptoms

Common ulcerative colitis symptoms include:[5][8]

• diarrhoea, often with blood, mucus or pus
• needing to go urgently or often, including at night
• feeling that you need to go even when your bowel is empty
• tummy pain
• bleeding from the bottom.

Other symptoms can include tiredness, a reduced appetite and weight loss.[5] During a flare-up, some people also have painful or swollen joints, mouth ulcers, red eyes or skin changes.[5]

Where the two conditions differ most

Location in the gut

This is the clearest difference. Crohn's disease can appear anywhere along the digestive tract, while ulcerative colitis is limited to the large bowel and rectum.[4] Because of this, Crohn's disease can affect how the small intestine absorbs nutrients, and it can cause problems around the anus.[3][4]

Pattern and depth of inflammation

In Crohn's disease, inflamed areas can sit next to healthy sections of bowel, and the inflammation can go deep into the bowel wall. In ulcerative colitis, the inflammation is continuous and affects the inner lining.[4] When a doctor looks inside the bowel and examines tissue samples, these patterns help tell the two conditions apart.[9][10]

Complications

Deeper inflammation means Crohn's disease can sometimes cause narrowing of the bowel (strictures) or abnormal channels between the bowel and nearby organs or skin (fistulas).[3][11] Long-standing ulcerative colitis is linked with a higher risk of bowel cancer, which is one reason people with ulcerative colitis are offered regular checks of the colon.[5]

What they have in common

Both conditions are thought to involve an abnormal immune reaction in the gut. Genes, the gut's bacteria and the environment may all play a part.[2][7] Both are more likely if a close relative has IBD, and smoking is linked with a higher chance of developing Crohn's disease.[1][7] Neither is thought to be caused by stress, although stress, infections and some medicines can trigger flare-ups.[5]

How doctors tell them apart

There's no single test for either condition.[3] A doctor will usually ask about your symptoms, medical and family history and the medicines you take, and examine you.[10] Tests may include:[3][5][9][10]

• Blood tests to look for anaemia, inflammation or infection.
• Stool tests to rule out infection and check for inflammation in the bowel, such as faecal calprotectin.[13]
• Colonoscopy, which uses a thin, flexible camera to look at the lining of the rectum and colon. Small tissue samples (biopsies) are taken and examined under a microscope.
• Gastroscopy, which looks at the food pipe, stomach and first part of the small intestine, if Crohn's disease higher up the gut is suspected.
• Scans such as MRI, CT or ultrasound, which can show parts of the small intestine that a camera can't easily reach.

Sometimes it isn't possible to say straight away which type of IBD someone has, and the picture becomes clearer over time.[3] Your doctor will explain which tests are suitable for you. Our article on gastroscopy vs colonoscopy explains what each test looks at, our colonoscopy patient guide covers what to expect, and our Colonoscopy and Gastroscopy page describes the endoscopy services at the clinic. Questions about arrangements for a test are covered at your consultation.

How treatment compares

Treatment for both conditions aims to calm inflammation, ease symptoms and keep the condition in remission.[11][12] The medicines used are often similar and may include:[3][5][11][12]

• aminosalicylates, such as mesalazine, which reduce inflammation and are used mainly in ulcerative colitis
• steroids, for short-term control of flare-ups
• immunosuppressants, which reduce the activity of the immune system
• biological and other targeted medicines, which act on specific parts of the immune response.

Surgery is an option for some people. In Crohn's disease, it may be used to remove a badly affected section of bowel or treat strictures and fistulas, but the condition can return elsewhere in the gut.[3][11] In ulcerative colitis, removing the colon and rectum is sometimes advised when symptoms are severe or medicines don't help.[5][12]

Your care team will also consider nutrition, since inflammation and diarrhoea can make it harder to get enough nutrients.[11] Care is long term and usually involves regular follow-up with a gastroenterologist. Dr Ling Khoon Lin trained in the management of inflammatory bowel disease at the University of Oxford; you can find out more about him on the specialist profile page.

When to see a doctor

See a doctor if you have:[3][5]

• diarrhoea that doesn't settle, or keeps coming back
• blood or mucus in your stool
• ongoing tummy pain
• weight loss without trying.

If you already have Crohn's disease or ulcerative colitis, contact your care team if your symptoms get worse or your treatment doesn't seem to be helping.[3]

Get urgent medical help (call 995 or go to the nearest Emergency Department) if you have:[5]

• severe tummy pain
• heavy or non-stop bleeding from the bottom, or large blood clots in your stool
• vomiting blood, or vomit that looks like coffee grounds.

Our article on blood in stool explains other common causes of bleeding. If you'd like to ask about an assessment, you can send a question through our contact form or request a consultation through the appointment form.

Frequently asked questions

What is the main difference between Crohn's disease and ulcerative colitis?

Crohn's disease can affect any part of the digestive tract, in patches and through the full thickness of the bowel wall. Ulcerative colitis affects only the colon and rectum, with continuous inflammation of the inner lining.[4][6]

Are Crohn's disease symptoms different from ulcerative colitis symptoms?

They overlap a lot. Both can cause diarrhoea, tummy pain, tiredness and weight loss. Bloody diarrhoea and urgency are especially common in ulcerative colitis, while Crohn's disease can also cause pain around the bottom and problems absorbing nutrients.[3][5][7]

Can ulcerative colitis turn into Crohn's disease?

They are separate conditions. But because they can look alike, a diagnosis is sometimes revised as more information becomes available from tests and how the condition behaves.[3]

Are Crohn's disease and ulcerative colitis the same as IBS?

No. Both are types of IBD, which causes inflammation and damage to the gut. IBS affects how the gut works without visible inflammation. See IBS vs IBD for more.[1]

Can Crohn's disease or ulcerative colitis be cured?

There's currently no medicine that cures Crohn's disease, but treatment can help people stay in remission for long periods.[3] For ulcerative colitis, treatment aims to relieve symptoms and prevent flare-ups; surgery to remove the colon is an option for some people with severe disease.[5][12]

Do I need a colonoscopy to find out which one I have?

A colonoscopy with biopsies is a key test for both conditions, often alongside blood tests, stool tests and scans.[9][10] Your doctor will advise which tests suit your symptoms, and you can ask about this at your consultation.

Sources

1. NHS. Inflammatory bowel disease (IBD). https://www.nhs.uk/conditions/inflammatory-bowel-disease/
2. Crohn's & Colitis UK. Understanding Crohn's and Colitis. https://crohnsandcolitis.org.uk/info-support/information-about-crohns-and-colitis/all-information-about-crohns-and-colitis/understanding-crohns-and-colitis
3. NHS. Crohn's disease. https://www.nhs.uk/conditions/crohns-disease/
4. MedlinePlus (US National Library of Medicine). Crohn's Disease. https://medlineplus.gov/crohnsdisease.html
5. NHS. Ulcerative colitis. https://www.nhs.uk/conditions/ulcerative-colitis/
6. MedlinePlus. Ulcerative Colitis. https://medlineplus.gov/ulcerativecolitis.html
7. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Symptoms & Causes of Crohn's Disease. https://www.niddk.nih.gov/health-information/digestive-diseases/crohns-disease/symptoms-causes
8. NIDDK. Symptoms & Causes of Ulcerative Colitis. https://www.niddk.nih.gov/health-information/digestive-diseases/ulcerative-colitis/symptoms-causes
9. NIDDK. Diagnosis of Crohn's Disease. https://www.niddk.nih.gov/health-information/digestive-diseases/crohns-disease/diagnosis
10. NIDDK. Diagnosis of Ulcerative Colitis. https://www.niddk.nih.gov/health-information/digestive-diseases/ulcerative-colitis/diagnosis
11. NIDDK. Treatment for Crohn's Disease. https://www.niddk.nih.gov/health-information/digestive-diseases/crohns-disease/treatment
12. NIDDK. Treatment for Ulcerative Colitis. https://www.niddk.nih.gov/health-information/digestive-diseases/ulcerative-colitis/treatment
13. MedlinePlus. Calprotectin Stool Test. https://medlineplus.gov/lab-tests/calprotectin-stool-test/